Our Ever-changing Butterfly Populations
by Ro Wauer
One of the fascinating facts about butterflies is their ever-changing populations. In any field or garden, butterfly species present may change significantly from one day or one week to the next. In a sense, the ever-changing population is one of the more exciting facets about butterfly-watching. In my garden at Mission Oaks near Mission Valley, probably a pretty good representation of the entire region, black swallowtails can be present for a few days and then totally disappear and pipevine swallowtails can be commonplace a few days later. And at about the same time, a few giant swallowtails put in their appearance. The butterfly scene can change dramatically.
Another population change that I have experienced in the last few weeks is the shift from cloudless sulphurs to large orange sulphurs. These two species are similar at first sighting, but the cloudless sulphur is usually lemon yellow with scattered white spots edged with red, while the large orange sulphur is orange-yellow with a dark line running from the tip to the center of the wing. Both perch with folded wings.
The reasons for changes in butterfly populations vary, but it primarily relates to emergence, the act of an adult butterfly leaving its chrysalis and flying free. Emergence depends upon weather conditions and time of year. Some species, such as falcate orangetips and Henry’s elfins, fly only in early spring. Others, such as soapberry and oak hairstreaks, appear a little later in spring. Still other species wait to emerge in late summer or fall. The emergence times depend so much upon when pertinent larval foodplants become available. In many cases, emergence can include dozens or even hundreds of individuals, thus significantly changing population numbers.
Almost any time of year, except during really cold periods in winter, I can pretty well depend on daily finding a few butterfly species in my yard. Some the more dependable species include little yellow, dusky-blue groundstreak, gray hairstreak, gulf fritillary, common buckeye, Carolina satyr, white and tropical checkered-skippers, and fiery skipper. Eastern tiger swallowtail, checkered white, orange and lyside sulphurs, southern dogface, great purple hairstreak, mallow scrub-hairstreak, Reakirt’s blue, queen, bordered patch, phaon and pearl crescents, question mark, common mestra, funereal duskywing, clouded and dun skippers, and Celia’s roadside-skipper, are also found year-round, but their appearance can never be expected.
Some of the late summer and fall species may be primarily composed of strays from further south, although because of the changing weather pattern, many of those that once were considered more tropical species are now able to find an adequate niche further north. During the last few years I have discovered several species that had not previously been recorded in the central Gulf Coastal area. Examples include yellow and white angled-sulphurs, Mexican yellow, tailed orange, Lacey’s and lantana scrub-hairstreaks, red-bordered metalmark, soldier, brown longtail, Mazans scallopwing, white-patched and violet-banded skippers, and Erichson’s white-skipper. How many of these latter species were able to find proper larval foodplants is anyone’s guess; only time will tell.
But perhaps the white-striped longtail, a long-tailed skipper with a white slash across the hindwing, best represents our changing butterfly populations. When I first established a garden to attract butterflies in the mid-1990’s, white-striped longtails were found only in the Lower Rio Grande Valley. But by 2000 and 2001 they were suddenly found almost daily during much of the year. Their larval foodplants – wild peas and other legumes - are plentiful in the area, and so they moved northward and are now recorded through much of coastal Texas. They are considered a true invader and now a highly successful resident. Ever garden should have one!